US20140354182A1 - Pixel and pixel circuit thereof - Google Patents

Pixel and pixel circuit thereof Download PDF

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Publication number
US20140354182A1
US20140354182A1 US14/160,878 US201414160878A US2014354182A1 US 20140354182 A1 US20140354182 A1 US 20140354182A1 US 201414160878 A US201414160878 A US 201414160878A US 2014354182 A1 US2014354182 A1 US 2014354182A1
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terminal
switch
driving transistor
voltage
pixel
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Li-Wei Liu
Wei-Chu Hsu
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AU Optronics Corp
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AU Optronics Corp
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    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
    • G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
    • G09G3/3208—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
    • G09G3/3225—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED] using an active matrix
    • G09G3/3233—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED] using an active matrix with pixel circuitry controlling the current through the light-emitting element
    • H05B33/0842—
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2300/00—Aspects of the constitution of display devices
    • G09G2300/08—Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
    • G09G2300/0809—Several active elements per pixel in active matrix panels
    • G09G2300/0814—Several active elements per pixel in active matrix panels used for selection purposes, e.g. logical AND for partial update
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2300/00—Aspects of the constitution of display devices
    • G09G2300/08—Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
    • G09G2300/0809—Several active elements per pixel in active matrix panels
    • G09G2300/0819—Several active elements per pixel in active matrix panels used for counteracting undesired variations, e.g. feedback or autozeroing
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/02—Improving the quality of display appearance
    • G09G2320/0233—Improving the luminance or brightness uniformity across the screen
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/04—Maintaining the quality of display appearance
    • G09G2320/043—Preventing or counteracting the effects of ageing
    • G09G2320/045—Compensation of drifts in the characteristics of light emitting or modulating elements

Definitions

  • the embodiment of the present invention relates generally to a basic electric circuit, and, more particularly, to a pixel and a pixel circuit thereof.
  • a compensating circuit may be arranged in the pixel to ameliorate the disadvantages associated with the above-mentioned problems, the disposition of a large quantity of transistors in the compensating circuit will result in a decrease in the aperture ratio of the pixel and in a reduced resolution.
  • the present disclosure provides a pixel and a pixel circuit thereof which address the problems faced by the prior art.
  • One aspect of the present disclosure is directed to a pixel that comprises an organic light-emitting diode, a driving transistor, a first switch, a third switch and a fourth switch.
  • the driving transistor is electrically coupled to the organic light-emitting diode.
  • the first switch is configured to write a data voltage into the control terminal of the driving transistor.
  • the fourth switch conducts the control terminal of the driving transistor and the first terminal, such that the control terminal of the driving transistor is charged and discharged via a current path, thereby forming a compensating voltage according to the voltage of the control terminal of the driving transistor.
  • the compensating voltage conducts the driving transistor and turns on the third switch, such that the driving current is provided to the organic light-emitting diode.
  • the pixel circuit comprises a first switch, a driving transistor, a third switch, a fourth switch and capacitor. Specifically, each of said driving transistor, first, third and fourth switches has a first terminal, a second terminal and a control terminal, while the capacitor has a first terminal.
  • the first terminal of the first switch is electrically coupled to a data voltage
  • the control terminal of the driving transistor is electrically coupled to the second terminal of the first switch
  • the second terminal of the third switch is electrically coupled to the first terminal of the driving transistor
  • the first terminal of the fourth switch is electrically coupled to the second terminal of the first switch
  • the second terminal of the fourth switch is electrically coupled to the first terminal of the driving transistor
  • the first terminal of the capacitor is electrically coupled to the second terminal of the first switch.
  • FIG. 1A schematically shows a pixel according to one embodiment of the present invention
  • FIG. 1B schematically shows a control waveform according to one embodiment of the present invention
  • FIG. 2A schematically shows a pixel according to one embodiment of the present invention
  • FIG. 2B schematically shows a control waveform according to one embodiment of the present invention
  • FIG. 3A schematically shows a pixel according to one embodiment of the present invention.
  • FIG. 3B schematically shows a control waveform according to one embodiment of the present invention.
  • FIG. 4A schematically shows a pixel according to one embodiment of the present invention.
  • FIG. 4B schematically shows a control waveform according to one embodiment of the present invention.
  • Couple means two or more elements are electrically contacted with one another, either directly or indirectly; while the terms “connect,” “connecting” and “connected” mean two or more elements are physically contacted with one another, either directly or indirectly. All these terms may be used to indicate the mutual operation or action of two or more elements.
  • the present disclosure provides a pixel structure, in conjunction with a three-stage control mode, so as to compensate for the voltage of a control terminal of a driving transistor in the pixel and thereby improve transistor variation, IR drop, and light-emitting diode aging. As a result, an improvement with respect to uneven brightness of the display panel is realized, and consequently, a high image quality of the display panel is maintained.
  • the pixel structure is illustrated in FIGS. 1A , 2 A and 3 A, while the three-stage control mode is shown in FIGS. 1B , 2 B and 3 B.
  • the following description, together with the drawings, is provided to explain the pixel structure and the three-stage control mode thereof.
  • the pixel 100 comprises a pixel circuit and an organic light-emitting diode 110 .
  • the pixel circuit comprises a first switch T 1 , a driving transistor T 2 , a third switch T 3 , a fourth switch T 4 and a capacitor C.
  • Each of the driving transistor T 2 , and the first, third and fourth switches (T 1 , T 3 and T 4 ) has a first terminal, a second terminal and a control terminal, while the capacitor C has a first terminal and a second terminal.
  • the first terminal of the first switch T 1 is electrically coupled to a data voltage Data
  • the control terminal of the driving transistor (or namely the second switch) T 2 is directly connected to the second terminal of the first switch T 1
  • the second terminal of the third switch T 3 is directly connected to the first terminal of the driving transistor T 2
  • the first terminal of the fourth switch T 4 is directly connected to the second terminal of the first switch T 1
  • the second terminal of the fourth switch T 4 is directly connected to the first terminal of the driving transistor T 2
  • the first terminal (or namely the first electrode) of the capacitor C is directly connected to the second terminal of the first switch T 1
  • the second terminal (or namely the second electrode) of the capacitor C is electrically coupled to a power source OVDD.
  • the second terminal of the fourth switch T 4 in addition to being directly connected to the first terminal of the driving transistor T 2 , is also directly connected to the second terminal of the third switch T 3 ; that is, the second terminal of the fourth switch T 4 is directly connected to the first terminal of the driving transistor T 2 and the second terminal of the third switch T 3 .
  • the first terminal of the capacitor C in addition to being directly connected to the second terminal of the first switch T 1 , is also directly connected to the first terminal of the fourth switch T 4 and the control terminal of the driving transistor T 2 ; that is, the first terminal of the capacitor C is directly connected to the second terminal of the first switch T 1 , the first terminal of the fourth switch T 4 and the control terminal of the driving transistor T 2 .
  • the first switch T 1 is controlled by a scan signal Scan
  • the driving transistor T 2 is controlled by a data voltage Data via the first switch T 1
  • the third switch (or namely the power source control switch) T 3 is controlled by an emitting signal EM
  • the fourth switch T 4 is controlled by a discharging signal DIS.
  • each of the driving transistor and switches can be a bipolar junction transistor (BJT), field-effect transistor (FET), insulated gate bipolar transistor (IGBT), etc., but the present disclosure is not limited in this regard.
  • BJT bipolar junction transistor
  • FET field-effect transistor
  • IGBT insulated gate bipolar transistor
  • the driving transistor and switches are field-effect transistors, in particular, N-type thin-film transistors (TFTs)
  • the second terminal of the driving transistor T 2 is directly connected to the anode of the light-emitting diode 110
  • the cathode of the light-emitting diode 110 is electrically connected to a reference voltage terminal OVSS
  • the first terminal of the third switch T 3 is electrically connected to a power source OVDD.
  • FIGS. 1A and 1B schematically shows a control waveform according to one embodiment of the present invention.
  • the scan signal Scan is a high-level signal, and therefore the first switch T 1 is turned on.
  • the first switch T 1 writes the data voltage Data into the control terminal of the driving transistor T 2 .
  • the voltage of the control terminal of the driving transistor T 2 is the data voltage Data.
  • the discharging signal DIS is also a high-level signal, and therefore, the fourth switch T 4 is turned on.
  • the emitting signal EM is a low-level signal, and the third switch T 3 remains turned off.
  • the present disclosure is not limited in this regard; that is, the first switch T 1 and the fourth switch T 4 may be turned on simultaneously.
  • the scan signal Scan is a low-level voltage while the discharging signal DIS is still a high-level signal, and hence the first switch T 1 is turned off while the fourth switch T 4 is turned on, thereby conducting the control terminal G of the driving transistor T 2 and the first terminal D.
  • the driving transistor T 2 acts like a diode, thereby forming a current path 120 , such that the data voltage Data of the control terminal of the driving transistor T 2 is discharged via the current path 120 , so that the data voltage Data of the control terminal of the driving transistor T 2 is discharged with a potential difference ⁇ V, thereby forming a compensating voltage (V Data ⁇ V).
  • the emitting signal EM is still a low-level signal, and hence the third switch T 3 is still turned off.
  • the emitting signal EM is a high-level signal and the discharging signal DIS is a low-level signal, such that the third switch T 3 is correspondingly turned on while the fourth switch T 4 is correspondingly turned off.
  • the scan signal Scan and data voltage Data are both low-level signals, and therefore the first switch T 1 is turned off.
  • the compensating voltage (V Data ⁇ V) conducts the driving transistor T 2 , and hence the driving current is provided to the organic light-emitting diode 110 via the driving transistor T 2 .
  • the third switch T 3 is turned on after the fourth switch T 4 has been turned off; however, the present disclosure is not limited in this regard, and the turning off of the fourth switch T 4 and the turning on of the third switch T 3 may happen at the same time.
  • I DS 1 2 ⁇ ⁇ ⁇ ⁇ C OX ⁇ ( W L ) ⁇ ( V GS - V th ) 2 ( 1 )
  • the data voltage Data of the control terminal of the driving transistor T 2 is discharged with a potential difference ⁇ V, thereby forming a compensating voltage (V Data ⁇ V).
  • V Data ⁇ V the potential difference
  • the V GS of the driving transistor T 2 is equal to V Data ⁇ V ⁇ V OLED ⁇ V OVSS .
  • the V GS of the driving transistor T 2 is substituted into formula (1) to obtain the following formula:
  • I DS 1 2 ⁇ ⁇ ⁇ ⁇ C OX ⁇ ( W L ) ⁇ ( V data - ⁇ ⁇ ⁇ V - V OLED - V OVSS - V th ) 2 ( 2 )
  • the compensating voltage may be automatically adjusted such that the driving current I OLED is maintained in a stable state, and the driving current I OLED is equal to the OLED emitting current. Accordingly, even when the pixel 100 encounters adverse conditions such as transistor variation, IR drop, light-emitting diode aging, etc., the driving current I OLED may be stably maintained, which in turn improves the evenness of the brightness for the display panel to thereby enhance the image quality of the display panel. Moreover, since the pixel 100 is only disposed with one driving transistor and three switches, the problems of low pixel aperture ratio and limited resolution associated with a large quantity of transistors disposed in the compensating circuit are ameliorated.
  • the compensating mechanism of the pixel circuit is such that when the circuit is operated in the compensating period (Comp.), the relationship between the level of the discharging potential difference ⁇ V and the level of the discharging amperage of the current path 120 is used to allow the automatic adjustment of the compensating voltage (V Data ⁇ V).
  • the detailed adjustment process is as follows: the control terminal of the driving transistor T 2 discharges the reference voltage terminal OVSS with a potential difference ⁇ V via the current path 120 , thereby forming the compensating voltage (V Data ⁇ V).
  • the amperage level is related to the threshold voltage V th of the driving transistor T 2 , the mobility ⁇ of the driving transistor T 2 , the voltage of the reference voltage terminal OVSS and the voltage of the OLED. Therefore, in a state where the conduction duration of the fourth switch T 4 is fixed, the compensating voltage (V Data ⁇ V) is automatically adjusted corresponding to the variation level of each factor.
  • the discharging current increases accordingly; that is, the potential difference ⁇ V increases, such that the driving current I OLED is maintained in a stable state.
  • the threshold voltage V th of the driving transistor T 2 increases, the discharging current decreases accordingly; that is, the potential difference ⁇ V decreases, such that the driving current I OLED is maintained in a stable state.
  • the second implementation of the pixel circuit structure differs from the first implementation in that the driving transistor and switches are field-effect transistors, and in particular, P-type thin-film transistors (TFTs).
  • the control terminal of the first switch T 1 is electrically connected to a scan signal Scan
  • the first terminal of the first switch T 1 is electrically connected to a data voltage Data
  • the first terminal of the driving switch (or namely the second switch) T 2 is electrically connected to the power source OVDD
  • the control terminal of the third switch (or the power source control switch) T 3 is electrically connected to the emitting signal EM
  • the first terminal of the third switch T 3 is directly connected to the anode of the light-emitting diode 210
  • the control terminal of the fourth switch T 4 is electrically connected to the discharging signal DIS
  • the first terminal of the fourth switch T 4 is directly connected to the first terminal of the driving switch T 2 and the second terminal of the third switch T 3
  • the second terminal of the capacitor C is
  • FIG. 2B illustrates a control waveform according to one embodiment of the present invention.
  • the scan signal Scan and the data voltage Data are both low-level signals, and hence the first switch T 1 is turned on. Therefore, the first switch T 1 writes the data voltage Data into the control terminal G of the driving transistor T 2 .
  • the voltage of the control terminal G of the driving transistor T 2 is the data voltage Data.
  • the discharging signal DIS is a low-level signal, and hence the fourth switch T 4 is turned on.
  • the emitting signal EM is a high-level signal, and as a result, the third switch T 3 is still turned off.
  • the fourth switch T 4 is turned on before the first switch T 1 is turned on.
  • the present disclosure is not limited in this regard; that is, the first switch T 1 and fourth switch T 4 can be turned on concurrently.
  • the scan signal Scan and the data voltage Data are both high-level voltages, and hence the first switch T 1 is turned off.
  • the discharging signal DIS is still a low-level signal, and therefore, the fourth switch T 4 is turned on, thereby conducting the control terminal G of the driving transistor T 2 and the first terminal D.
  • the emitting signal EM is still a high-level signal, such that the third switch T 3 is still turned off.
  • the driving transistor T 2 acts like a diode, thereby forming a current path 220 , such that the control terminal of the driving transistor T 2 is charged via the current path 220 .
  • the power source OVDD charges the data voltage Data of the control terminal of the driving transistor T 2 , such that the data voltage Data of the control terminal of the driving transistor T 2 is increased by a potential difference ⁇ V, thereby forming the compensating voltage (V Data + ⁇ V), wherein the potential difference ⁇ V is in direct proportion to the charging current level.
  • the emitting signal EM is a low-level signal
  • the discharging signal DIS is a high-level signal
  • the third switch T 3 is correspondingly turned on
  • the fourth switch T 4 is correspondingly turned off.
  • the scan signal Scan and the data voltage Data are both high-level voltages, and hence the first switch T 1 is still turned off.
  • the third switch T 3 is turned on after the fourth switch T 4 has been turned off.
  • the present disclosure is not limited in this regard; that is, the turning off of the fourth switch T 4 and the turning on of the third switch T 3 may happen simultaneously.
  • the compensating voltage (V Data + ⁇ V) conducts the driving transistor T 2 , and hence, the driving current is provided to the organic light-emitting diode 210 via the driving transistor T 2 .
  • I DS 1 2 ⁇ ⁇ ⁇ ⁇ C OX ⁇ ( W L ) ⁇ ( V SG - V th ) 2 ( 3 )
  • the data voltage Data of the control terminal G of the driving transistor T 2 is increased by a potential difference ⁇ V, thereby forming the compensating voltage (V Data + ⁇ V).
  • the V SG of the driving transistor T 2 is equal to V OVDD ⁇ V Data ⁇ V.
  • the V SG of the driving transistor T 2 is substituted into formula (3), thereby obtaining the following formula:
  • I DS 1 2 ⁇ ⁇ ⁇ ⁇ C OX ⁇ ( W L ) ⁇ ( V OVDD - V Data - ⁇ ⁇ ⁇ V - V th ) 2 ( 4 )
  • the compensating voltage can be automatically adjusted such that the driving current I OLED is maintained in a stable state.
  • the compensating mechanism of the pixel circuit is such that when the circuit is operated in the compensating period (Comp.), the relationship between the level of the charging potential difference ⁇ V and the level of the charging amperage of the current path 220 is used to allow the automatic adjustment of the compensating voltage (V Data + ⁇ V).
  • the detailed adjustment process is as follows: the power source OVDD charges the control terminal of the driving transistor T 2 with a potential difference ⁇ V via the current path 220 , thereby forming the compensating voltage (V Data + ⁇ V).
  • the amperage level is related to the threshold voltage V th of the driving transistor T 2 , the mobility ⁇ of the driving transistor T 2 , and the voltage of the power source OVDD. Therefore, under the condition that the conduction duration of the fourth switch T 4 is fixed, the compensating voltage (V Data + ⁇ V) is automatically adjusted corresponding to the variation level of each factor.
  • the charging current increases accordingly; that is, the potential difference ⁇ V increases, such that the driving current I OLED is maintained in a stable state.
  • the third implementation of the pixel circuit structure differs from the first implementation in that the driving transistor and switches are field-effect transistors, in particular, P-type thin-film transistors (TFTs), the second terminal of the driving transistor T 2 is directly connected to the cathode of the light-emitting diode 310 , and the first terminal of the third switch T 3 is electrically connected to the reference voltage terminal OVSS.
  • the driving transistor and switches are field-effect transistors, in particular, P-type thin-film transistors (TFTs)
  • TFTs P-type thin-film transistors
  • the control terminal of the first switch T 1 is electrically connected to a scan signal Scan
  • the first terminal of the first switch T 1 is electrically connected to a data voltage Data
  • the second terminal of the driving switch (or namely the second switch) T 2 is directly connected to the cathode of the light-emitting diode 310
  • the control terminal of the third switch (or the power source control switch) T 3 is electrically connected to an emitting signal EM
  • the first terminal of the third switch T 3 is electrically connected to a reference voltage source OVSS
  • the control terminal of the fourth switch T 4 is electrically connected to a discharging signal DIS
  • the first terminal of the fourth switch T 4 is directly connected to the first terminal of the driving switch T 2 and the second terminal of the third switch T 3
  • the second terminal of the capacitor C is electrically connected to power source OVDD
  • the first terminal of the capacitor C is directly connected to the second terminal of the first switch T 1 , the control terminal of the driving switch T 2 and the second terminal of the fourth switch T
  • FIG. 3B illustrates a control waveform according to one embodiment of the present invention.
  • the scan signal Scan and the data voltage Data are both low-level signals, and hence the first switch T 1 is turned on. Therefore, the first switch T 1 writes the data voltage Data into the control terminal G of the driving transistor T 2 . At this time, the voltage of the control terminal G of the driving transistor T 2 is the data voltage Data.
  • the discharging signal DIS is a low-level signal, and hence the fourth switch T 4 is turned on.
  • the emitting signal EM is a high-level signal, and as a result, the third switch T 3 is still turned off.
  • the fourth switch T 4 is turned on before the first switch T 1 is turned on.
  • the present disclosure is not limited in this regard; that is, the first switch T 1 and fourth switch T 4 can be turned on concurrently.
  • the scan signal Scan and the data voltage Data are both high-level voltages, and hence the first switch T 1 is turned off.
  • the discharging signal DIS is still a low-level signal, and therefore, the fourth switch T 4 is turned on, thereby conducting the control terminal G of the driving transistor T 2 and the first terminal D.
  • the emitting signal EM is still a high-level signal, such that the third switch T 3 is still turned off.
  • the driving transistor T 2 acts like a diode, thereby forming a current path 320 , such that the power source OVDD charges the control terminal G of the driving transistor T 2 via the current path 320 .
  • the power source OVDD charges the data voltage Data of the control terminal of the driving transistor T 2 , such that the data voltage Data of the control terminal G of the driving transistor T 2 is increased by a potential difference ⁇ V, thereby forming the compensating voltage (V Data + ⁇ V).
  • the emitting signal EM is a low-level signal, and hence the third switch T 3 is correspondingly is turned on, while the discharging signal DIS is a high-level signal, and hence the fourth switch T 4 is correspondingly turned off.
  • the scan signal Scan and the data voltage Data are both high-level voltages, and hence the first switch T 1 is still turned off.
  • the compensating voltage (V Data + ⁇ V) conducts the driving transistor T 2 , and hence, the driving current is provided to the organic light-emitting diode 310 via the driving transistor T 2 .
  • the third switch T 3 is turned on after the fourth switch T 4 has been turned off.
  • the present disclosure is not limited in this regard; that is, the turning off of the fourth switch T 4 and the turning on of the third switch T 3 may happen simultaneously.
  • the characteristics of the pixel 300 according to the present embodiment are discussed with reference to the current formula of the thin-film transistor. Said current formula is the same as the formula (3) described hereinabove, and hence, will not be recreated below.
  • the data voltage Data of the control terminal of the driving transistor T 2 is increased by a potential difference ⁇ V, thereby forming the compensating voltage (V Data + ⁇ V).
  • the V SG of the driving transistor T 2 is equal V OVDD ⁇ V OLED ⁇ V Data ⁇ V. Subsequently, the V SG of the driving transistor T 2 is substituted into formula (3), thereby obtaining the following formula:
  • I DS 1 2 ⁇ ⁇ ⁇ ⁇ C OX ⁇ ( W L ) ⁇ ( V OVDD - V OLED - V Data - ⁇ ⁇ ⁇ V - V th ) 2 ( 5 )
  • the compensating voltage can be automatically adjusted such that the driving current I OLED is maintained in a stable state.
  • the compensating mechanism of the pixel circuit is such that when the circuit is operated in the compensating period (Comp.), the relationship between the level of the charging potential difference ⁇ V and the level of the charging amperage of the current path 320 is used to allow the automatic adjustment of the compensating voltage.
  • the detailed adjustment process is as follows: the power source OVDD charges the control terminal of the driving transistor T 2 with a potential difference ⁇ V via the current path 320 , thereby forming the compensating voltage (V Data + ⁇ V). Since the potential difference ⁇ V is in direct proportion to the level of the charging amperage, the amperage level is related to the threshold voltage V th of the driving transistor, the mobility ⁇ of the driving transistor, the voltage of the power source OVDD and the voltage of the OLED. Therefore, under the condition that the conduction duration of the fourth switch T 4 is fixed, the compensating voltage (V Data + ⁇ V) is automatically adjusted corresponding to the variation level of each factor.
  • the charging current increases accordingly; that is, the potential difference ⁇ V increases, such that the driving current I OLED is maintained in a stable state.
  • FIG. 4A schematically shows a pixel according to one embodiment of the present invention.
  • the second terminal of the capacitor C of the pixel 400 in FIG. 4A is electrically coupled to the reference voltage terminal OVSS.
  • the anode of the organic light-emitting diode 410 in FIG. 4A is electrically connected to the power source OVDD, and the cathode of the light-emitting diode 410 is electrically connected to the first terminal of the third switch T 3 .
  • FIG. 4B illustrates a control waveform according to one embodiment of the present invention.
  • the control waveform herein is identical to the control waveform in FIG. 1 B.
  • the operations of the pixel 400 in FIG. 4A are similar to that of the pixel 100 in FIG. 1A .
  • a current path 420 is also formed in the pixel 400 .
  • the data voltage Data of the control terminal of the driving transistor T 2 is discharged via the current path 420 , so that the data voltage Data of the control terminal of the driving transistor T 2 is discharged with a potential difference ⁇ V, thereby forming a compensating voltage (V Data ⁇ V).
  • the compensating voltage (V Data ⁇ V) may be automatically adjusted such that the driving current I OLED is maintained in a stable state. Accordingly, even when the pixel 400 as illustrated in FIG. 4A encounters adverse conditions such as transistor variation, IR drop, light-emitting diode aging, etc., the driving current I OLED may be stably maintained, which in turn improves the evenness of the brightness for the display panel to thereby enhance the image quality of the display panel. Moreover, since the pixel 400 is only disposed with one driving transistor and three switches, the problems of low pixel aperture ratio and limited resolution associated with a large quantity of transistors disposed in the compensating circuit are ameliorated.
  • Embodiments of the present disclosure provide a pixel and pixel circuit to address the problems of uneven brightness and poor quality of the display panel that are associated with transistor variation, IR drop, light-emitting diode aging, etc. Further, since the pixel is only disposed with one driving transistor and three switches, the problems of low pixel aperture ratio and limited resolution associated with a large quantity of transistors disposed in the compensating circuit are ameliorated.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Electroluminescent Light Sources (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)
  • Control Of El Displays (AREA)
US14/160,878 2013-05-30 2014-01-22 Pixel and pixel circuit thereof Abandoned US20140354182A1 (en)

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TW102119130A TWI479467B (zh) 2013-05-30 2013-05-30 畫素及其畫素電路

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TWI515712B (zh) * 2014-05-28 2016-01-01 友達光電股份有限公司 畫素補償電路
TWI554997B (zh) * 2015-03-10 2016-10-21 友達光電股份有限公司 畫素結構
CN104658485B (zh) * 2015-03-24 2017-03-29 京东方科技集团股份有限公司 Oled驱动补偿电路及其驱动方法
CN104933993B (zh) 2015-07-17 2017-12-08 合肥鑫晟光电科技有限公司 像素驱动电路及其驱动方法、显示装置
TWI569248B (zh) * 2016-02-18 2017-02-01 友達光電股份有限公司 畫素電路以及驅動方法
TWI569249B (zh) * 2016-07-01 2017-02-01 友達光電股份有限公司 畫素電路
TWI682381B (zh) * 2018-10-17 2020-01-11 友達光電股份有限公司 畫素電路、顯示裝置及畫素電路驅動方法
CN109671398B (zh) 2019-02-28 2020-05-15 厦门天马微电子有限公司 像素驱动电路的驱动方法、显示面板和显示装置
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TW201445538A (zh) 2014-12-01

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